<!DOCTYPE html>
<html>
	<head>
		<meta charset="UTF-8">
		<title></title>
	</head>
	<body>
		<script>
			var shi="窗前明月光，疑是地上霜";
			alert(shi.length);
			alert(shi.indexOf("光"));
			alert(shi.substring(2,4));
		</script>
	</body>
</html>
